A semiconductor wafer is polished to achieve a flat surface required for fabricating of today's advanced semiconductor devices. One way to effectively polish a semiconductor wafer involves a chemical mechanical polishing system. The polishing system typically includes a silicon carbide (SiC) block for mounting a wafer thereon and a polishing pad. Both the SiC block and the polishing pad are rotatable. As the SiC block and the polishing pad rotate, the wafer, which is mounted on the block, is pressed against the polishing pad. A solution of silica and potassium hydroxide (KOH) is applied to the surface of the polishing pad. The friction created between the polishing pad and the wafer, in combination with the applied solution, smoothes the etched surface of the wafer.
Important characteristics in a polished wafer are thickness uniformity, smoothness and flatness of the wafer surface. However, polishing pads degrade over time producing wafers of lesser quality. Wafers having non-uniform surfaces are sometimes caused by the surface of the polishing pad being rough, especially when the pad has been used a number of times. Thus, during the life of the polishing pad, it has become necessary to dress the polishing surface of the pad so that the wafers produced using the pad are more uniform, flat and smooth. One way to dress a polishing pad is by smoothing the polishing surface of the pad using an abrasive dressing element.
An example of an apparatus and method of dressing a polishing pad is disclosed in U.S. Pat. No. 6,976,907. The apparatus includes a cylindrical dressing member (i.e., conditioning piece) that is rotatable about an imaginary axis of rotation that is generally parallel to the polishing surface. A polishing pad surface metrology system is used to address particular non-uniformity on the polishing surface of the polishing pad and provide a uniform polishing pad surface. In other words, the polishing pad surface is analyzed to determine where and how the surface should be dressed.